Hitherto, image displaying methods using technologies such as an electrophoretic method, an electrochromic method, thermal method and dichromatic particle rotation method have been proposed instead of the liquid crystal display (LCD) method. The purpose of these methods is to obtain merits such as that wide viewing angle is near that of usual printed matters, electric consumption is low and the display medium has a memorizing ability, compared with the LCD. Therefore, such the media can be considered as next generation display medium with low cost and are expected to be developed in the field of display for portable terminals or electronic paper.
Moreover, an electrophoretic method is recently proposed, in which dispersion composed of dispersed particles and colored liquid is placed between facing substrates. However, the electrophoretic method has problems such as that the particles are easily precipitated so that the stability of the dispersed state is difficultly maintained since particles having high specific gravity such as titanium oxide are dispersed in a liquid having low specific gravity and stability of repeatedly displaying images is lacking because durability for long term is low since a dye is used for coloring the liquid. As a countermeasure of the above problems, a method is proposed for seemingly not appearing such the problems by enclosing the dispersion in microcapsules but the problems are not solved yet. Furthermore, it is also a problem that the density is not correctively displayed since the boundary of touching portion of the microcapsules occupies relatively large area when the system is viewed from outside.
On the other hand, a method is proposed, in which charged particles are moved in gas. The problems caused in the electrophoretic method such as precipitation or coagulation of the particles are solved in this method. However, much higher driving voltage is necessary to move the particles in comparison with the electrophoretic method, and it is an obstacle to use in so called electric paper and so on.
A technology is required to transport and incorporating charged particles in an image display medium for a preparation of image display medium in which charged particles are moved in gas. A method is proposed in which particles are adhered onto substrate by a spray gun employing a principle of an electric coating, for example, as described in Patent Publication 1.
Proposed is another method in which charged particles are made as an aerosol state and are moved by an electric field force formed by electrodes, for example, as described in Patent Publication 2.
Proposed is the other method in which charged particles are provided to the surface of the substrate, and excess amount of the particles are removed by mechanical function such as a pressure plate or blade to leave necessary amount of particles on the substrate, for example, as described in Patent Publication 23.
However it is difficult to control the moving amount of the particles charge amount of the moved particles accurate as expected, display characteristics are not attained as expected, a clear image having sufficient density and contrast is not obtained as the result.
Thus a technology to obtain an image display medium for a use of, for example, electric paper is not sufficient.
Patent Publication 1: JP A 2003-241231
Patent Publication 2: JP A 2004-184632
Patent Publication 3: JP A 2005-266641